Method for tracing gram-negative bacteria inside animal model using stable and bioluminescence-based expression system therefor

ABSTRACT

A method of creating a biotechnological product and an efficient and stable bio-luminescence vector which could be used for tracking Gram-negative bacteria when distributing inside animal body are provided. Through conjugation, this auto-luminescence vector can be easily transmitted from bacteria to bacteria among Gram-negative bacteria, and may facilitate bacteria to be luminescence-labeled for subsequently analyzing the dynamic change of bio-luminescent bacteria within animal body in vivo. This system includes a lacZ promoter-driven luxABCDE, a high copy number of ColE1 replicon, and a high plasmid stability of the conjugative and broad host-ranged plasmid pSE34 from  Salmonella enterica  serovar  Enteritidis  Sal550. This resulting construct pSE-Lux1 can not only conjugatively transmit among bacteria with broad host range, but also stably maintain in bacteria to efficiently express the bio-luminescent luxABCDE without supplementing the subtract for luciferases and the antibiotics for plasmid selection.

“This application is a divisional application of application Ser. No. 12/895,849, filed on Oct. 1, 2010, the entire contents of which are incorporated by reference.”

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to methods for generating bioluminescence-labeled Gram-negative bacteria in order to overcome the drawback of the difficulty to tracking the bacteria inside their hosts, because it offers a powerful tool to tracking Gram-negative bacteria in vivo using a stably and highly bioluminescence expressing plasmid vehicle.

2. Description of Related Art

For observing bacterial distribution and behavior inside the animal body, it conventionally needs the sacrifices of the experimental animals and the analyses of animal organ specimens. Therefore, an ideal method using light-emitting (bioluminescent) gene expression system of bacterial luxABCDE has been developed to observe the dynamic changes of bacterial distribution and behavior without animal sacrifice while bacteria existing inside their host bodies.

Although many methods have been previously provided to study the bacterial behavior and distribution inside their host bodies using light-emitting gene expression in bacteria, there are still certain drawbacks to limit their applications. They are as the follows: (i) the plasmids used to express the bioluminescence could not stably exist in bacteria without any selection stress, as a result of plasmid loss after couple generation; (ii) the delivery method, such as electroporation or competence, is common to transfer plasmid into bacterium, and however, it is restricted by bacterial capsule, which is composited of polysaccharides and can be a crucial barrier to limit the bacterial transformation to very low rate; (iii) the transposons utilized to insert the bioluminescence gene marker into bacterial chromosome usually transpose randomly into uncertain transposition site with unacceptably low transposition rate, and therefore the resulting individuals are different, and difficult to select and to confirm whether their insertion sites are crucial for further characteristic analysis; and (iv) the double crossing-over replacement applied to insert a marker at a specific site in chromosome needs many tedious cloning, and worse, its replacement efficiency is very poor.

Additionally, the bioluminescence genes obtained via transposition or gene replacement are just a single copy in bacterial chromosome, which might not be expressed as highly as in a high copy number of plasmid, such as the plasmid containing ColE1 replication origin. Thus, the need for improvement still exists.

SUMMARY OF THE INVENTION

It is therefore one object of the invention to provide a method for tracing Gram-negative bacteria inside animal model using stable and bioluminescence-based expression system therefor in order to directly observe and detect the dynamic change of steady bioluminescence bacteria inside animal, we built an in vivo-detectable bioluminescence plasmid in Gram-negative bacteria, which can stably exist and efficiently express luciferase genes in Gram-negative bacteria with high copy number.

By utilizing the invention the following advantages can be obtained: Ability to express the bioluminescence genes luxABCDE in Gram-negative bacteria under control by the promoter region of lacZ operon. Efficient expression of the bioluminescence gene luxABCDE contributed by high copy number of ColE1 plasmid replication origin. Steady existence of the bioluminescent luxABCDE-carried plasmid in Gram-negative bacteria due to the built-in pir, parG, parF, stbD, and stbE from the plasmid pSE34 of Salmonella enterica serotype Enteritidis. Feasible convenience to transmit the bioluminescent luxABCDE-carried plasmid among the Gram-negative bacteria by conjugation using the genes pilX1, pilX2, pilX4, pilX5, pilX6, pilX7, pilX8, pilX9, pilX10, pilX11, taxA, taxB, and taxC from the plasmid pSE34 of Salmonella enterica serotype Enteritidis.

The above and other objects, features and advantages of the invention will become apparent from the following detailed description taken with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart according to the invention;

FIG. 2A schematically depicts plasmid pXen-5 of the invention;

FIG. 2B schematically depicts plasmid p3ZLux4 of the invention;

FIG. 3A schematically depicts plasmid pSE34 of the invention;

FIG. 3B schematically depicts plasmid pSE-Lux1 of the invention;

FIG. 4 schematically depicts plasmid pSE-Lux1 of the invention; and

FIG. 5 is a table showing plasmid stability tests of p3Zlux4 and pSE-Lux1 according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 to 3B, a flow chart and plasmids in accordance with the invention are illustrated.

Steps of constructing this steady auto-bioluminescence plasmid of the invention are as the follow:

(a) To clone a promoterless luxABCDE into a promoter-containing vector, so as to express the genes luxABCDE from the promoter.

(b) To clone both at least one ColE1 replication origin and at least one drug resistance gene into a plasmid pSE34.

(c) To merge the two clones from steps (a) and (b) together, so as to obtain a vector with the features of auto-bioluminescence, plasmid stability, and high copy number.

Processes of the invention are discussed in detail below:

(a) Construction of p3ZLux4 (10)

The promoterless luxABCDE-ken from a pXen-5 was cut and inserted into a pGEM3-Zf+ using a Pstl as cloning sites based on the Escherichia coli cloning system, where luxABCDE genes can be expressed through the control of a lacZ promoter of pGEM3-Zf+.

Plasmid the pXen-5, is 18,357 bp long, and comprises a 5,655-bp promoterless luxABCDE and kanamycin-resistant gene ken. The luxA and luxB are luciferase-encoding genes, and luxC, luxD, and luxE encode lipid acid reductases. LuxC, LuxD, and LuxE can catalyze the reduction of long chain lipid acids, and generate aldehyde compounds, which may be the substrates for LuxA and LuxB luciferases to react and emit light.

Plasmid the pGEM3-Zf+, a 3,199-bp, comprises a ampicillin resistant gene amp, ColE1 replication origin, and a lacZ operon. The lacZ operon constitutes of a promoter, which may promote the downstream gene expression, multiple cloning site, and beta-galactosidase-encoding gene lacZ.

The resulting clone is 11,766-bp p3ZLux4, which is a high copy number, ampicillin resistant, and luxABCDE expression vector; however, it can not stably maintain inside bacteria for long time period without ampicillin selection.

(b) Construction of pBS-SE34 (11)

Plasmid pSE34 from the native Salmonella enterica serotype Enteritidis SE550 phage type PT34, 32,950 kb, was cut and inserted into a pBlueScript II KS (+/−) at Xbal site, and its insertion direction was determined by DNA sequencing. The resulting clone is named pBS-SE34.

S. enterica serotype Enteritidis SE550 phage type PT34 is the secondary dominant phage type, and its emerging is due to the presence of conjugative pSE34 (SEQ ID NO 2). This plasmid pSE34 comprises genes pir, parG, parF, stbD, and stbE, which facilitates the equal partition of plasmids into two daughter cells while bacterial cell division. Therefore, pSE34 can stably exist inside bacteria without any selection. In addition, pSE34 comprises genes pilX1, pilX2, pilX4, pilX5, pilX6, pilX7, pilX8, pilX9, pilX10, pilX11, taxA, taxB, and taxC, which may play the role of plasmid dissemination among Gram-negative bacteria through conjugation system.

Plasmid pBlueScript II KS (+/−), 2,961-bp long, comprises high copy number of ColE1 replication origin, ampicillin resistant gene, and multiple cloning sites in lacZ operon.

Therefore, the resulting clone pBS-SE34, 34.6 kb, has the features of high copy number, conjugation, and plasmid stability.

(c) Construction of pSE-Lux1 (12)

Plasmid p3ZLux4 and pBS-SE34 were cut by SalI and Xhol, respectively. The two cut DNA fragments were ligated together. The resulting clone is named pSE-Lux1, 46.3 kb. The plasmid pSE-Lux1 has the features of high copy number, high plasmid stability, auto-bioluminescence, and broad host-ranged conjugation for Gram-negative bacteria.

Referring to FIG. 4 in conjunction with FIGS. 1 to 3B, plasmid pSE-Lux1 of the invention is discussed in detail below. The auto-bioluminescence plasmid pSE-Lux1 (SEQ ID NO 1) of the invention specific for Gram-negative bacteria comprises at least one luxABCDE gene (SEQ ID NO 21), at least one promoter of luxABCDE gene, at least one high copy number of ColE1 replication origin, at least one drug-resistant gene, at least one gene pir (SEQ ID NO 3), at least one gene parG (SEQ ID NO 4), at least one gene parF (SEQ ID NO 5), at least one gene stbD (SEQ ID NO 6), at least one gene stbE (SEQ ID NO 7), at least one gene pilX1 (SEQ ID NO 8), at least one gene pilX2 (SEQ ID NO 9), at least one gene pilX4 (SEQ ID NO 10), at least one gene pilX5 (SEQ ID NO 11), at least one gene pilX6 (SEQ ID NO 12), at least one gene pilX7 (SEQ ID NO 13), at least one gene pilX8 (SEQ ID NO 14), at least one gene pilX9 (SEQ ID NO 15), at least one gene pilX10 (SEQ ID NO 16), at least one gene pilX11 (SEQ ID NO 17), at least one gene taxA (SEQ ID NO 18), at least one gene taxB (SEQ ID NO 19), and at least one gene taxC (SEQ ID NO 20).

Among those genes in pSE-Lux1, the promoter of luxABCDE gene is PlacZ (SEQ ID NO 22) from lacZ operon.

Among those genes in pSE-Lux1, the drug-resistant gene may be ampicillin resistant, kanamycin resistant, or ampicillin and kanamycin resistant.

Among those genes in pSE-Lux1, pir, parG, parF, stbD, and stbE genes are associated with plasmid partition, which can stabilize plasmids to be equally distributed toward two daughter cells.

Among those genes in pSE-Lux1, pilX1, pilX2, pilX4, pilX5, pilX6, pilX7, pilX8, pilX9, pilX10, pilX11, taxA, taxB, and taxC are associated with plasmid conjugation, and they may facilitate for the gene cloning and plasmid transmission from one bacterium to another, such as to deliver a conjugative plasmid from Salmonella enterica to Escherichia coli.

Among those genes in pSE-Lux1, the luxABCDE comprises luxA, luxB, luxC, luxD, and luxE. Genes luxA and luxB are luciferase-encoding genes, and luxC, luxD, and luxE encode lipid acid reductases. LuxC, LuxD, and LuxE can catalyze the reduction of long chain lipid acids, and their products are aldehyde compounds.

The aldehydes are the substrates for LuxA and LuxB luciferases to react and emit light. Therefore, it is no need to add any substrate for luciferases to emit light.

Because the pSE-Lux1 in the invention can not only independently assist bacteria to appear bioluminescent, but also steady exist inside bacteria, the advantage of the invention is good for direct observation and detection of the dynamic changes while the bioluminescence bacteria existing inside animals.

Referring to FIG. 5, a plasmid stability test according to the invention is discussed in detailed below.

Two clones with p3Zlux4 and pSE-Lux1 in E. coli and S. enterica Typhimurium LBNP4471, respectively, were continuously cultured in LB (Luria-Bertani) broth without any supplementation, such as antibiotics. After 79 generation, they were plated onto both LB agar and LB agar with the supplementation of ampicillin and kanamycin in order to count the bacterial cell counts (colony formation units, CFU). The results as shown in FIG. 5 show that there were 76.3% (1550/2030) colonies remaining the resistance to ampicillin and kanamycin in the case of pSE-Lux1, whereas only 8.8×10-4% in the case of p3Zlux4. It means that pSE-Lux1 has much better stability than p3ZLux4 as high as around hundred thousand folds. In addition, all of colonies from the LB agar with the supplementation of ampicillin and kanamycin can appear bioluminescence, indicating that plasmid pSE-Lux1 can stably exit in Gram-negative bacteria and efficient express the bioluminescence gene luxABCDE.

While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims. 

1. A method of creating a steady bioluminescence vector which has DNA sequences listed in SEQ ID NO 1 and used for Gram-negative bacteria comprising steps of: (a) cloning a promoterless luxABCDE that comes from a vector pXen-5 into a promoter-containing vector to express the genes luxABCDE, wherein the gene expression of luxABCDE is controlled through a lacZ promotor of a plasmid pGEM3-Zf+; (b) cloning a conjugative plasmid pSE34 with a plasmid pBlueScript II KS (+/−) that has at least one ColE1 replication origin and at least one drug resistance gene; and (c) ligating said merging the two clones from steps (a) and (b) together so as to obtain the bioluminescence vector which has the DNA sequence listed in SEQ ID NO:1 with the features of auto-bioluminescence, plasmid stability, conjugation and a high copy number. 